Fuel Oil Compositions

ABSTRACT

A method of improving the low temperature properties of a fuel oil and minor amounts of (a) at least one polar nitrogen compound effective and (b) at least one polyamine detergent is disclosed. The method involves adding to the composition (c) at least one acidic organic species.

This invention relates to improvements in fuel oil compositions, and more especially to fuel oil compositions containing detergent species and susceptible to wax formation at low temperatures.

Fuel oils, whether derived from petroleum or from vegetable sources, contain components, e.g., n-alkanes or methyl n-alkanoates, that at low temperature tend to precipitate as large, plate-like crystals or spherulites of wax in such a way as to form a gel structure which causes the fuel to lose its ability to flow. The lowest temperature at which the fuel will still flow is known as the pour point.

As the temperature of a fuel falls and approaches the pour point, difficulties arise in transporting the fuel through lines and pumps. Further, the wax crystals tend to plug fuel lines, screens, and filters at temperatures above the pour point. These problems are well recognised in the art, and various additives have been proposed, many of which are in commercial use, for depressing the pour point of fuel oils. Similarly, other additives have been proposed and are in commercial use for reducing the size and changing the shape of the wax crystals that do form. Smaller size crystals are desirable since they are less likely to clog a filter. The wax from a diesel fuel, which is primarily an alkane wax, crystallizes as platelets. Certain additives inhibit this and cause the wax to adopt an acicular habit, the resulting needles being more likely to pass through a filter, or form a porous layer of crystals on the filter, than are platelets. Other additives may also have the effect of retaining the wax crystals in suspension in the fuel, reducing settling and thus also assisting in prevention of blockages. These types of additives are often termed ‘wax anti-settling additives’ (WASA) and are commonly polar nitrogen species.

Many additives have been described over the years for enhancing engine cleanliness, e.g. for reducing or removing deposits in the intake system (e.g. carburettors, intake manifold, inlet vales) or combustion chamber surfaces of spark-ignition engines, or for reducing or preventing injector nozzle fouling in compression-ignition engines.

For example, UK Patent specification No 960,493 describes the incorporation of metal-free detergents, in the form of polyolefin-substituted succinimides of tetraethylene pentamine, in base fuels for internal combustion engines. The use of such metal-free detergents is now widespread. Most commonly used are polyisobutylene substituted succinimides which are the reaction products of polyisobutylene substituted acylating agents such as succinic acid or anhydride with polyamines. Such materials and their methods of production will be known to those skilled in the art.

The trend in modern diesel engine technology is to increase power output and efficiency by increasing injection pressures and decreasing injector nozzle diameters. Under these conditions, the build up of injector deposits is more likely and the deposition which occurs is more severe. This has led fuel manufacturers to produce new types of fuels which are often sold as ‘premium’ grades and promoted as being especially effective to improve engine cleanliness. To meet this performance claim, such premium fuels usually contain significantly higher levels of detergent than non-premium grade fuels.

Whilst largely effective with regard to engine cleanliness, a drawback has been identified with the use of high levels of detergent in fuel oils. Specifically, it has been observed that the presence of high levels of polyamine detergent species in premium grade fuels can interfere with the cold-flow performance of wax anti-settling additives when these are also present in the fuel. So, although the fuel may be satisfactory from an engine cleanliness viewpoint, its low temperature properties, in terms of wax anti-settling and cold filter plugging point (CFPP) may not be adequate.

The present invention is based on the discovery that the additional presence of a third co-additive species can restore the low temperature properties of the fuel containing a wax anti-settling additive and a polyamine detergent.

WO95/03377 describes that certain fuel additives not known for providing improvements in low temperature properties can nevertheless be beneficial to such properties when combined with copolymeric ethylene flow improvers. Oil soluble ashless dispersants are disclosed as one such class of fuel additives. Further additives including wax anti-settling additives may additionally be incorporated.

EP 0 104 015 A describes that certain carboxylic acids, preferably aromatic acids such as benzoic acid, can be used to improve the solubility of certain wax anti-settling additives when they are combined together in a fuel additive concentrate. At least one mole of acid is required per mole of wax anti-settling additive.

Thus in accordance with a first aspect, the present invention provides a method of improving the low temperature properties of a fuel oil composition comprising a major amount of a fuel oil and minor amounts of (a) at least one polar nitrogen compound effective as a wax anti-settling additive and (b) at least one polyamine detergent, the method comprising adding to the composition (c) at least one acidic organic species.

In accordance with a second aspect, the present invention provides the use of (c) at least one acidic organic species to improve the low temperature properties of a fuel oil composition; wherein the fuel oil composition comprises a major amount of a fuel oil and minor amounts of (a) at least one polar nitrogen compound effective as a wax anti-settling additive and (b) at least one polyamine detergent.

In accordance with a third aspect, the present invention provides the use of (e) at least one acidic organic species to substantially restore a loss in low temperature properties of a fuel oil comprising (a) at least one polar nitrogen compound effective as a wax anti-settling additive, such loss being attributable to the presence of (b) at least one polyamine detergent in the fuel oil.

In accordance with a fourth aspect, the present invention provides a process of ameliorating a negative interaction on the low temperature performance of (a) a polar nitrogen compound effective as a wax anti-settling additive attributable to its use in combination with (b) at least one polyamine detergent, the process comprising:

-   -   (i) determining for a fuel oil composition comprising a major         amount of a fuel oil and minor amounts of (a) and (b), the         amounts of (a) and (b) such that the low temperature properties         of the fuel oil composition are inferior to the low temperature         properties of a fuel oil composition comprising the same amount         of (a) in the absence of (b); and,     -   (ii) determining all amount of (c) at least one acidic organic         species, which when added to the fuel oil composition is such         that the low temperature properties of the fuel oil composition         are improved; and,     -   (iii) manufacturing a fuel oil composition comprising (a), (b)         and (c) in the amounts determined in (i) and (ii).

The observed loss in wax anti-settling and CFPP performance appears to be limited to the use of polyamine detergents in combination with WASA components. It is noteworthy that a similar loss in performance is not observed when non-polyamine detergents are used in combination with WASA components. The addition of the acidic organic species mitigates this loss in performance allowing higher levels of polyamine detergents to be used together with WASA species without compromising the low temperature properties of the additised fuel.

As indicated above, the combined presence in a fuel oil of a polyamine detergent and a WASA may lead to a reduction in performance in terms of wax anti-settling and/or CFPP. With regard to the first and second aspects, an improvement in the low temperature properties can refer to an improvement in terms of either wax anti-settling performance, an improvement in CFPP or preferably an improvement in both properties. The restoration of a loss in low temperature properties of the third aspect and the amelioration of a negative interaction of the fourth aspect will be understood in the same context.

Thus in the first and second aspects, the invention requires that eider or both, preferably both, of the wax anti-settling behaviour and the CFPP of the fuel oil is improved when (c) is present compared to the situation where (c) is absent. It should be noted that it is not required that either property necessarily reaches the level which would be expected without the presence of (b).

In the third aspect, the use of (c) should return either or both, preferably both, of the wax anti-settling behaviour and the CFPP of the fuel oil to the level which would be expected without the presence of (b). The use of the term ‘substantially restore’ should be taken to include the situation where, although the precise numerical value of the property may not be regained, the difference is not practically significant. Of course, the situation where the use of (c) leads to better low temperature properties than would be expected without the presence of (b) is also included in the scope of the third aspect.

The fourth aspect should be taken in the same context as the first and second aspects. That is, it is not required that either the wax anti-settling performance or the CFPP of the fuel oil composition manufactured in step (iii) necessarily reaches the level which would be expected without the presence of (b), but simply that at least one property, preferably both, are improved relative to those determined in step (i).

The various features of the invention, which are applicable to all aspects, will now be described in more detail.

(a) The Polar Nitrogen Compound Effective as a Wax Anti-Settling Additive.

Such species are known in the art.

Preferred are oil-soluble polar nitrogen compounds carrying one or more, preferably two or more, substituents of the formula >NR¹³, where R¹³ represents a hydrocarbyl group containing 8 to 40 atoms, which substituent or one or more of which substituents may be in the form of a cation derived therefrom. The oil soluble polar nitrogen compound is generally one capable of acting as a wax crystal growth inhibitor in fuels. It comprises for example one or more of the following compounds:

An amine salt and/or amide formed by reacting at least one molar proportion of a hydrocarbyl-substituted amine with a molar proportion of a hydrocarbyl acid having from 1 to 4 carboxylic acid groups or its anhydride, the substituent(s) of formula >NR¹³ being of the formula —NR¹³R¹⁴ where R¹³ is defined as above and R¹⁴ represents hydrogen or R¹³, provided that R¹³, and R¹⁴ may be the same or different, said substituents constituting part of the amine salt and/or amide groups of the compound.

Ester/amides may be used, containing 30 to 300, preferably 50 to 150, total carbon atoms. These nitrogen compounds are described in U.S. Pat. No. 4,211,534. Suitable amines are predominantly C₁₂ to C₄₀ primary, secondary, tertiary or quaternary amines or mixtures thereof but shorter chain amines may be used provided the resulting nitrogen compound is oil soluble, normally containing about 30 to 300 total carbon atoms. The nitrogen compound preferably contains at least one straight chain C₈ to C₄₀, preferably C₁₄ to C₂₄, alkyl segment.

Suitable amines include primary, secondary, tertiary or quaternary, but are preferably secondary. Tertiary and quaternary amines only form amine salts. Examples of amines include tetradecylamine, cocoamine, and hydrogenated tallow amine. Examples of secondary amines include di-octadecylamine, di-cocoamine, di-hydrogenated tallow amine and methylbehenyl amine. Amine mixtures are also suitable such as those derived from natural materials. A preferred amine is a secondary hydrogenated tallow amine, the alkyl groups of which are derived from hydrogenated tallow fat composed of approximately 4% C₁₄, 31% C₁₆, and 59% C₁₈.

Examples of suitable carboxylic acids and their anhydrides for preparing the nitrogen compounds include ethylenediamine tetraacetic acid, and carboxylic aids based on cyclic skeletons, e.g., cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid and naphthalene dicarboxylic acid, and 1,4-dicarboxylic acids including dialkyl spirobislactones. Generally, these acids have about 5 to 13 carbon atoms in the cyclic moiety. Preferred acids useful in the present invention are benzene dicarboxylic acids, e.g. phthalic acid, isophthalic acid, and terephthalic acid. Phthalic acid and its anhydride are particularly preferred. The particularly preferred compound is the amide-amine salt formed by reacting 1 molar portion of phthalic anhydride with 2 molar portions of dihydrogenated tallow amine.

Other examples are long chain alkyl or alkylene substituted dicarboxylic acid derivatives such as amine salts of monoamides of substituted succinic acids, examples of which are known in the art and described in U.S. Pat. No. 4,147,520, for example. Suitable amines may be those described above.

Other examples are condensates, for example, those described in EP-A-327423.

Other examples of polar nitrogen compounds are compounds containing a ring system carrying at least two substituents of the general formula below on the ring system

-A-NR¹⁵R¹⁶

where A is a linear or branched chain aliphatic hydrocarbylene group optionally interrupted by one or more hetero atoms, and R¹⁵ and R¹⁶ are the same or different and each is independently a hydrocarbyl group containing 9 to 40 atoms optionally interrupted by one or more hetero atoms, the substituents being the same or different and the compound optionally being in the form of a salt thereof. Advantageously, A has from 1 to 20 carbon atoms and is preferably a methylene or polymethylene group. Such compounds are described in WO 93/04148 and WO9407842.

Other examples are the free amines themselves as these are also capable of acting as wax crystal growth inhibitors in fuels. Suitable amines including primary, secondary tertiary or quaternary, but are preferably secondary. Examples of amines include tetradecylamine, cocoamine, and hydrogenated tallow amine. Examples of secondary amines include di-octadecylamine, di-cocoamine, di-hydrogenated tallow amine and methylbehenyl amine, Amine mixtures are also suitable such as those derived from natural materials. A preferred amine is a secondary hydrogenated tallow amine, the alkyl groups of which are derived from hydrogenated tallow fat composed of approximately 4% C₁₄, 31% C₁₆, and 59% C₁₈.

(b) The Polyamine Detergent.

A preferred class of polyamine detergents are those made by reacting an acylating agent having a hydrocarbyl substituent of at least 10 carbon atoms and a nitrogen compound characterized by the presence of at least one —NH— group. Typically, the acylating agent will be a mono- or polycarboxylic acid (or reactive equivalent thereof) such as a substituted succinic or propionic acid and the amino compound will be a polyamine or mixture of polyamines, most typically, a mixture of ethylene polyamines. The amine also may be a hydroxyalkyl-substituted polyamine. The hydrocarbyl substituent in such acylating agents preferably averages at least about 30 or 50 and up to about 200 carbon atoms.

Illustrative of hydrocarbyl substituent groups containing at least 10 carbon atoms are n-decyl, n-dodecyl, tetrapropenyl, n-octadecyl, oleyl, chlorooctadecyl, triicontanyl, etc. Generally, the hydrocarbyl substituents are made from homo- or interpolymers (e.g. copolymers, terpolymers) of mono- and di-olefins having 2 to 10 carbon atoms, such as ethylene, propylene, 1-butene, isobutene, butadiene, isoprene, 1-hexene, 1-octene, etc. Typically, these olefins are 1-monoolefins. This substituent can also be derived from the halogenated (e.g. chlorinated or brominated) analogs of such homo- or interpolymers.

The hydrocarbyl substituents are predominantly saturated. The hydrocarbyl substituents are also predominantly aliphatic in nature, that is they contain no more than one non-aliphatic moiety (cycloalkyl, cycloalkenyl or aromatic) group of 6 or less carbon atoms for every 10 carbon atoms in the substituent. Usually, however, the substituents contain no more than one such non-aliphatic group for every 50 carbon atoms, and in many cases, they contain no such non-aliphatic groups at all; that is, the typically substituents are purely aliphatic. Typically, these purely aliphatic substituents are alkyl or alkenyl groups.

A preferred source of the substituents are poly(isobutene)s obtained by polymerization of a C₄ refinery stream having a butene content of 35 to 75 weight percent and isobutene content of 30 to 60 weight percent in the presence of a Lewis acid catalyst such as aluminum trichloride or boron trifluoride. These polybutenes predominantly contain monomer repeating units of the configuration —C(CH₃)₂CH₂—.

The hydrocarbyl substituent is attached to the succinic acid moiety or derivative thereof via conventional means, for example the reaction between maleic anhydride and an unsaturated substituent precursor such as a polyalkene, as described for example in EP-B-0 451 380.

One procedure for preparing the substituted succinic acylating agents involves first chlorinating the polyalkene until there is an average of at least about one chloro group for each molecule of polyalkene. Chlorination involves merely contacting the polyalkene with chlorine gas until the desired amount of chlorine is incorporated into the chlorinated polyalkene. Chlorination is generally carried out at a temperature of about 75° C. to about 125° C. If desired, a diluent can be used in the chlorination procedure. Suitable diluents for this purpose include poly- and perchlorinated and/or fluorinated alkanes and benzenes.

The second step in the procedure is to react the chlorinated polyalkene with the maleic reactant at a temperature usually within the range of about 100° C. to about 200° C. The mole ratio of chlorinated polyalkene to maleic reactant is usually about 1:1. However, a stoichiomeic excess of maleic reactant can be used, for example, a mole ratio of 1:2. If an average of more than about one chloro group per molecule of polyalkene is introduced during the chlorination step, then more than one mole of maleic reactant can react per molecule of chlorinated polyalkene. It is normally desirable to provide an excess of maleic reactant; for example, an excess of about 5% to about 50%, for example 25% by weight. Unreacted excess maleic reactant may be stripped from the reaction product, usually under vacuum.

Another procedure for preparing substituted succinic acid acylating agents utilizes a process described in U.S. Pat. No. 3,912,764 and U.K. Pat. No. 1,440,219. According to that process, the polyalkene and the maleic reactant are first reacted by heating them together in a direct alkylation procedure. When the direct alkylation step is completed, chlorine is introduced into the reaction mixture to promote reaction of the remaining unreacted maleic reactants. According to the patents, 0.3 to 2 or more moles of maleic anhydride are used in the reaction for each mole of polyalkene. The direct alkylation step is conducted at temperatures to 180° C. to 250° C. During the chlorine-introducing stage, a temperature of 160° C. to 225° C. is employed.

The attachment of the hydrocarbyl substituent to the succinic moiety may alternatively be achieved via the thermally-driven ‘ene’ reaction, in the absence of chlorine. Use of such a material a the acylating agent leads to products having particular advantages; for example, chlorine-free products having excellent detergency and lubricity properties. In such products, the reactant is preferably formed from a polyalkene having at least 30% preferably 50% or more such as 75% of residual unsaturation in the form of terminal, e.g. vinylidene, double bonds.

Suitable polyamines are those comprising amino nitrogens linked by alkylene bridges, which amino nitrogens may be primary, secondary and/or tertiary in nature. The polyamines may be straight chain, wherein all the amino groups will be primary or secondary groups, or may contain cyclic or branched regions or both, in which case tertiary amino groups may also be present. The alkylene groups are preferably ethylene or propylene groups, with ethylene being preferred. Such materials may be prepared from the polymerization of lower alkylene diamines such as ethylene diamine, a mixture of polyamines being obtained, or via the reaction of dichloroethane and ammonia.

Specific examples of the polyalkylene polyamines (1) are ethylene diamine, tetra(ethylene)pentamine, tri-(trimethylene)tetramine and 1,2-propylene diamine. Specific examples of hydroxyalkyl-substituted polyamines include N-(2-hydroxyethyl)ethylene diamine, N,N¹-bis-(2-hydroxyethyl)ethylene diamine, N-(3-hydroxybutyl) tetramethylene diamine, etc. Specific examples of the heterocyclic-substituted polyamines (2) are N-2-aminoethyl piperazine, N-2 and N-3 amino propyl morpholine, N-3-(dimethylamino) propyl piperazine, 2-heptyl-3-(2-aminopropyl) imidazoline, 1,4-bis(2-aminoethyl)piperazine, 1-(2-hydroxy ethyl)piperazine, and 2-heptadecyl-1-(2-hydroxyethyl)-imidazoline, etc. Specific examples of the aromatic polyamines (3) are the various isomeric phenylene diamines, the various isomeric naphthalene diamines, etc.

Many patents have described suitable polyamine detergents including U.S. Pat. Nos. 3,172,892; 3,219,666; 3,272,746; 3,310,492; 3,341,542; 3,444,170; 3,455,831; 3,455,832; 3,576,743; 3,630,904; 3,632,511; 3,804,763 and 4,423,435, and including European patent applications EP 0 336 664 and EP 0 263 703. A typical and preferred compound of this class is that made by reacting a poly(isobutylene)-substituted succinic anhydride acylating agent (e.g. anhydride, acid, ester, etc.) wherein the poly(isobutene) substituent has between about 50 to about 200 carbon atoms with a mixture of ethylene polyamines having 3 to about 10 amino nitrogen atoms per ethylene polyamine and about 1 to about 6 ethylene groups.

The polyamine component may be defined by the average numrber of nitrogen atoms per molecule of the component, which may preferably be in the range of 4 to 8.5, more preferably 6.8 to 8, especially 6.8 to 7.5 nitrogens per molecule.

Also suitable are materials made from amine mixtures comprising polyamines having seven and eight, and optionally nine, nitrogen atoms per molecule (so-called ‘heavy’ polyamines).

Preferably, the polyamine mixture comprises at least 45% and preferably 50% by weight of polyamines having seven nitrogen atoms per molecule, based on the total weight of polyamines. In addition to polyamine mixtures, single species may also be used, for example TEPA and TETA.

A preferred polyamine detergent comprises the reaction product between a poly(isobutene) substituted succinic anhydride acylating agent with a polyamine or mixture of polyamines as hereinbefore described. Preferably, the poly(isobutene) has a number average molecular weight (Mn) of about 400-2500, preferably 400-1300, such as about 950.

(c) The Acidic Organic Species.

A range of acidic organic species have been found to be effective in the present invention.

One class of species are unsaturated, monocarboxylic acids, particularly aliphatic acids having between 8 and 30 carbon atoms. Preferred in this class are the fatty acids, preferably fatty acids with 12 to 22 carbon atoms. Examples include lauric acid, palmitoleic acid, oleic acid, elaidic acid, petroselic acid, ricinoleic acid, elaeostearic acid, linoleic acid, linolenic acid, gadoleic acid, or erucic acid. Mixtures of fatty acids such as those obtained from natural sources are also suitable. Examples include rape-seed oil fatty acid, soya fatty acid and tall oil fatty acid.

Saturated carboxylic acids are also suitable with the proviso that saturated acids containing straight-chains of 10 or more carbon atoms have been found not to be effective. Non-limiting examples include acetic acid, propionic acid, butyric acid,

Acids, if unsaturated, may be linear or branched. Saturated acids, provided that the proviso above is applied may be linear, or they may be branched. Non-limiting examples of branched acids include neodecanoic acid and neo-tridecoanoic acid.

Polycarboxylic acids are also suitable, for example hydrocarbyl-substituted succinic acids or dimer, trimer and higher oligomer acids derived from fatty acids.

Acids comprising aromatic ring systems are also suitable. Non-limiting examples include benzoic acid, salicylic acid and similar.

Non-aromatic, cyclic acids may be used. These may be single rings or used ring structures and may contain unsaturation. Non-limiting examples include naphthenic acids and resin acids such as abietic acid, dihydroabietic acid, tetrahydroabietic acid, dehydroabietic acid, neoabietic acid, pimaric acid, levopimaric acid, parastrinic acid and similar.

In a preferred embodiment, the acidic organic species comprises an unsaturated, monocarboxylic acid having between 8 and 30 carbon atoms, preferably between 12 and 22 carbon atoms.

The Fuel Oil

The fuel oil may be, e.g., a petroleum-based fuel oil, especially a middle distillate fuel oil. Such distillate fuel oils generally boil within the range of from 110° C. to 500° C., e.g., 150° C. to 400° C.

The invention is applicable to middle distillate fuel oils of all types, including the broad-boiling distillates, i.e., those having a 90%-20% boiling temperature difference, as measured in accordance with ASTM D-86, of 50° C. or more.

The fuel oil may comprise atmospheric distillate or vacuum distillate, cracked gas oil, or a blend in any proportion of straight run and thermally and/or catalytically cracked distillates. The most common petroleum distillate fuels are kerosene, jet fuels, diesel fuels, heating oils and heavy fuel oils. The heating oil may be a straight atmospheric distillate, or may also contain vacuum gas oil or cracked gas oil or both. The fuels may also contain major or minor amounts of components derived from the Fischer-Tropsch process. Fischer-Tropsch fuels, also known as FT fuels, include those that are described as gas-to-liquid fuels, coal and/or biomass conversion fuels. To make such fuels, syngas (CO+H₂) is first generated ad then converted to normal paraffins and olefins by a Fischer-Tropsch process. The normal paraffins may then be modified by processes such as catalytic cracking/reforming or isomerisation, hydrocracking and hydroisomerisation to yield a variety of hydrocarbons such as iso-paraffins, cyclo-paraffins and aromatic compounds. The resulting FT fuel can be used as such or in combination with other fuel components and fuel types such as those mentioned in this specification. The above mentioned low temperature flow problem is most usually encountered with diesel fuels and with heating oils. The invention is also applicable to fuel oils containing fatty acid methyl esters derived from vegetable oils, for example, rapeseed methyl ester, either used alone or in admixture with a petroleum distillate oil.

The fuel oil is preferably a low sulphur content fuel oil. Typically, the sulphur content of the fuel oil will be less than 500 ppm (parts per million by weight). Preferably, the sulphur content of the fuel will be less than 100 ppm, for example, less than 50 ppm. Fuel oils with even lower sulphur contents, for example less that 20 ppm or less than 10 ppm are also suitable.

Treat Rates

The amounts of each component present in the fuel oil will depend on the nature of the species used, the properties of the fuel oil and the low temperature performance required. As discussed hereinabove, the present invention is based on the observation of a negative impact on the low temperature behaviour of the wax anti-settling additive when present in premium diesel fuels which contain relatively high levels of polyamine detergent.

Typically, the amount of (b) at least one polyamine detergent in the fuel oil composition will be in excess of 50 ppm by weight based on the weight of the fuel oil, for example in excess of 75 ppm by weight or 100 ppm by weight. Some premium diesel fuels may contain up to 500 ppm by weight of polyamine detergent. This can be compared to a treat rate of around 10-75 ppm for more conventional, non-premium diesel fuels.

The amount of (a) at least one polar nitrogen compound effective as a wax anti-settling additive will typically be in the range of 10-300 ppm, preferably 10-100 ppm by weight based on the weight of the fuel oil.

The amount of (c) used will typically be in the range of 5-200, preferably, 5-150, more preferably 5-100, for example 10-50 ppm by weight based on the weight of the fuel oil.

Other Additives

It is commonplace in the art to use polar nitrogen compounds effective as a wax anti-settling additives in combination with other additional cold-flow improving additives. Suitable materials will be well known to those skilled in the art and include for example, ethylene-unsaturated ester copolymers such as EVA and similar polymers. The present invention contemplates the addition of such additional cold-flow improving additives; their application in terms of treat rate being also well known to those skilled in the art. In an embodiment of all aspects of the invention, the fuel oil further comprises an ethylene-unsaturated ester copolyner.

Evaluation of Low Temperature Properties.

The method of the first aspect, the uses of the second and third aspects and the process of the fourth aspect all require that the low temperature properties of the fuel oil composition be measured. As is known in the art, there are a number of methods which can be used to determine the low temperature properties of a fuel oil. Preferably, the low temperature properties are as determined by measuring ΔCP, CFPP, or both. Preferably, the low temperature properties improved in all aspects of the present invention are ΔCP, CFPP, or both.

ΔCP is a measurement of the propensity of the wax content of a fuel oil to settle and thus a determination of the effectiveness of a wax anti-settling additive. To determine ΔCP, the cloud point (CP) of a base fuel oil is measured. The wax anti-settling additive under study is then added to the base fuel and the sample cooled to a temperature below the measured CP. This temperature may vary, in Germany a temperature of −13° C. is commonly used, in South Korea it may be −15 or −20° C. and a value of −18° C. is also often used. After leaving the fuel oil sample for a time to allow any wax to settle, the CP of the bottom 20% by volume of the sample is measured. The difference between this measurement and the value obtained for the base fuel is ΔCP. A small value, preferably around zero, of ΔCP indicates good wax dispersancy.

CFPP is a standard industry test to evaluate the ability of a fuel oil sample to flow through a filter at reduced temperature. The test which is carried out by the procedure described in detail in “Jn. Of the Institute of Petroleum”, vol. 52, No. 510 (1996), pp 173-285, is designed to correlate with the cold flow of a middle distillate in automotive diesels. In brief, a sample of the oil to be tested (40 cm³) is cooled in a bath which is maintained at about −34° C. to give linear cooling at about 1° C./min. Periodically (at each one degree centigrade starting from above the cloud point), the oil is tested for its ability to flow through a fine screen in a prescribed time period using a test device which is a pipette to whose lower end is attached an inverted funnel which is positioned below the surface of the oil to be tested. Stretched across the mouth of the funnel is a 350 mesh screen having an area defined by a 12 mm diameter. The periodic tests are initiated by applying a vacuum to the upper end of the pipette whereby oil is drawn through the screen up into the pipette to a mark indicating 20 cm³ of oil. After each successful passage, the oil is returned immediately to the CFPP tube. The test is repeated with each one degree drop in temperature until the oil fails to fill the pipette within 60 seconds, the temperature at which failure occurs being reported as the CFPP temperature.

The present invention encompasses a method for improving the low temperature properties of a fuel oil composition comprising adding at least one acidic organic species to a fuel oil composition; wherein the fuel oil composition comprises a major amount of a fuel oil and minor amounts of (a) at least one polar nitrogen compound effective as a wax anti-settling additive and (b) at least one polyamine detergent.

The present invention encompasses a method for restoring a loss in low temperature properties of a fuel oil comprising adding at least one acidic organic species comprising at least one polar nitrogen compound to a faet oil.

The invention will now be described by way of example only.

In the experiments detailed below, a low-sulphur content diesel fuel containing a fixed amount (48 ppm) of a polar nitrogen compound effective as a wax anti-settling additive and varying amounts of a polyamine detergent was tested for ΔCP and CFPP. The effect of adding various amounts of an acidic organic species was determined.

The polar nitrogen compound effective as a wax anti-settling used was an N,N-dialkylammonium salt of 2-N′,N′dialkylamidobenzoate, the product of reacting one mole of phthalic hydride and two moles of di(hydrogenated tallow) amine.

The polyamine detergent used was a PIBSA-PAM detergent, the product of reacting a polyisobutylene-substituted succinic anhydride, the polyisobutylene group having a molecular weight of ca. 1000, with a polyamine mixture predominating in species having at least seven nitrogen atoms per molecule.

For all tests, the diesel fuel also contained fixed amounts of additional cold-flow additives. These are typical of additives routinely used in commercial diesel fuels and were mainly ethylene-unsaturated ester co-polymers and fumarate vinyl acetate co-polymers. All amounts are given in ppm of active ingredient (i.e. ingredient which is not solvent or carrier) by weight, based on the weight of the fuel.

For the wax anti-settling tests, the fuel was cooled to −18° C.

Table 1 below gives results showing the effect of an acidic organic species comprising a mixture of fatty acids predominating in straight-chain C18 mono- and di-unsaturated mono-carboxylic acids.

TABLE 1 Example detergent/ppm acid/ppm CFPP/° C. ΔCP/° C. 1 0 0 −26.5 0.6 2 84 0 −23.7 3.3 3 108 0 −23.5 6.4 4 127 0 −20.0 8.1 5 0 10 −24.5 0.4 6 84 10 −24.5 0.6 7 108 10 −25.8 1.2 8 127 10 −23.0 1.4 9 0 25 −27.0 0.3 10 84 25 −25.0 0.9 11 127 25 −22.5 0.9 12 0 50 −25.0 1.1 13 84 50 −23.0 0.5 14 127 50 −23.0 1.0 15 0 100 −23.5 0.3 16 84 100 −25.5 0.8 17 127 100 −22.0 1.4 18 108 125 −29.0 1.6 19 0 150 −26.5 0.6 20 84 150 −23.0 1.0 21 127 150 −22.0 1.7

From Table 1, it can be seen that in the absence of the organic acidic species, increasing amounts of detergent lead to a general decrease in CFPP and a marked increase in ΔCP (Comparative Examples 1-4). This demonstrates the loss in low-temperature properties associated with the combined use of the WASA with the polyamine detergent. The addition of the acid in the absence of the detergent had some effect on CFPP but no noticeable effect on ΔCP (compare Examples 1, 5, 9, 12, 15 & 19). The data in the table clearly show that the addition of the acid to the fuel in the presence of the detergent and the WASA mitigates the loss in low-temperature properties. For example, compare Example 2 with Examples 6, 10, 13, 16 & 20 which all contain 84 wppm of detergent, or Example 4 with Examples 8, 11, 14, 17 & 21 which alt contain 127 wppm of detergent.

In Table 2 below, the acid used was a neodecanoic acid. All other species were the same as used in Table 1.

TABLE 2 Example detergent/ppm acid/ppm CFPP/° C. ΔCP/° C. 1 0 0 −26.5 0.6 2 84 0 −23.7 3.3 3 108 0 −23.5 6.4 4 127 0 −20.0 8.1 22 0 25 −26.0 0.2 23 84 25 −21.5 0.7 24 127 25 −25.0 4.6 25 0 100 −27.0 0.2 26 84 100 −24.0 1.0 27 127 100 −23.0 3.9

The results of Table 2 show a similar trend to those of Table 1.

Table 3 shows the results for several other organic acids. As with Tables 1 and 2, all show an improvement in either CFPP, ΔCP or both compared to Comparative Examples 1-4.

TABLE 3 Example detergent/ppm Acid (*)/ppm CFPP/° C. ΔCP/° C. 1 0 0 −26.5 0.6 2 84 0 −23.7 3.3 3 108 0 −23.5 6.4 4 127 0 −20.0 8.1 28 0 (A) 150 −28.0 0.3 29 84 (A) 150 −23.0 0.5 30 127 (A) 150 −24.0 0.6 31 108 (D) 10 −25.0 1.5 32 108 (D) 60 −28.5 2.9 33 108 (D) 125 −29.5 1.5 34 108 (E) 60 −28.5 3.0 35 108 (E) 125 −27.0 2.9 36 108 (F) 15 −23.0 2.8 37 108 (F) 30 −22.5 2.3 38 108 (F) 60 −26.5 2.9 39 108 (F) 125 −28.5 2.8 40 108 (G) 60 −25.5 1.3 41 108 (G) 125 −24.0 1.0 42 108 (H) 10 −24.5 4.6 43 0 (I) 25 −24.5 0.2 44 84 (I) 25 −22.5 0.7 45 127 (I) 25 −21.5 2.0 46 0 (J) 75 −29.0 0.6 47 84 (J) 75 −24.0 1.0 48 127 (J) 75 −20.0 2.8 [*(A) = propionic acid, (D) = oleic acid, (E) = linoleic acid, (F) = Tall oil fatty acid, (G) = soya fatty acid, (H) = salicylic acid, (I) = dodecyl succinic acid (J) = polyisobutylene succinic diacid] 

1. A method of improving the low temperature properties of a fuel oil composition comprising a major amount of a fuel oil and minor amounts of (a) at least one polar nitrogen compound effective as a wax anti-settling additive and (b) at least one polyamine detergent comprising adding at least one acidic organic species to the fuel oil.
 2. A method according to claim 1 wherein, the at least one polar nitrogen compound comprises an oil-soluble polar nitrogen compound carrying one or more substituents of the formula >NR¹³, where R¹³ represents a hydrocarbyl group containing 8 to 40 atoms, which substituent or one or more of which substituents may be in the form of a cation derived therefrom.
 3. A method according to claim 1 wherein, the at least one polar nitrogen compound comprises an amide-amine salt formed by reacting 1 molar portion of phthalic anhydride with 2 molar portions of dihydrogenated tallow amine.
 4. A method according to claim 1 wherein, the at least one polyamine detergent comprises the reaction product between a poly(isobutene) substituted succinic anhydride acylating agent with a polyamine or mixture of polyamines.
 5. A method according to claim 4 wherein the poly(isobutene) has a number average molecular weight (Mn) ranging from 400-2500.
 6. A method according to claim 1 wherein the acidic organic species comprises an unsaturated, monocarboxylic acid having between 8 and 30 carbon atoms.
 7. A method according to claim 1 wherein the low temperature properties improved are ΔCP, CFPP or both.
 8. A method for improving the low temperature properties of a fuel oil composition comprising adding at least one acidic organic species to a fuel oil composition; wherein the fuel oil composition comprises a major amount of a fuel oil and minor amounts of (a) at least one polar nitrogen compound effective as a wax anti-settling additive and (b) at least one polyamine detergent.
 9. A method for restoring a loss in low temperature properties of a fuel oil comprising adding at least one acidic organic species comprising at least one polar nitrogen compound to a fuel oil.
 10. A process of ameliorating a negative interaction on the low temperature performance of (a) a polar nitrogen compound effective as a wax anti-settling additive attributable to its use in combination with (b) at least one polyamine detergent, the process comprising: (i) determining for a fuel oil composition comprising a major amount of a fuel oil and minor amounts of (a) and (b), the amounts of (a) and (b) such that the low temperature properties of the fuel oil composition are inferior to the low temperature properties of a fuel oil composition comprising the same amount of (a) in the absence of (b); and, (ii) determining an amount of (c) at least one acidic organic species, which when added to the fuel oil composition is such that the low temperature properties of the fuel oil composition are improved; and, (iii) manufacturing a fuel oil composition comprising (a), (b) and (c) in the amounts determined in (i) and (ii). 